Polypropylene resins are excellent in mechanical strength, rigidity, heat resistance, chemical resistance, oil resistance, transparency, low-temperature impact resistance, etc., and utilizing these properties, they have been widely used for packaging materials or covering materials, such as films, sheets and bottles, or decorative materials such as wall paper. Such polypropylene resins, however, have high permeability to gases such as oxygen, and therefore, they could not be used for packaging materials required to have high gas barrier properties, such as those for foods, pharmaceuticals, cosmetics, etc.
Accordingly, in order to enhance gas barrier properties of polypropylene resins, there has been proposed a method of laminating a resin having more excellent gas barrier properties than these resins, such as polyamide or an ethylene/vinyl acetate copolymer saponification product, onto a polypropylene resin. In this case, the bond strength between the polypropylene resin and polyamide (sometimes referred to as “PA” hereinafter) or an olefin/vinyl acetate copolymer saponification product (sometimes referred to as “EVOH” hereinafter) is markedly low, and therefore, it has been proposed that various bonding resins, such as an ionomer, an ethylene/vinyl acetate copolymer and graft-modified products of carboxylic acids, are co-extruded to produce a multilayer structure (patent literature 1).
In recent years, increase in size of productive facilities and speeding up have been further promoted, and materials having more excellent molding processability than before have been required. However, when the molding rate is increased or the laminate is subjected to stretch molding, there sometimes occur problems that the bond strength between PA or EVOH and a bonding resin is weakened, and EVOH and the bonding resin are liable to be peeled from each other, resulting in lowering of barrier properties and deterioration of appearance.
Accordingly, there has been desired development of a modified polypropylene composition for forming laminates, which enables prevention of lowering of interlaminar bond strength even in the case where a laminate thereof is produced at a high speed or a laminate thereof is subjected to stretch molding, and a laminate using the composition and having excellent interlaminar bond properties.